TRIPOLI (AFP) - UN special envoy to Libya Abdul-Ilah al-Khatib arrived in Tripoli Sunday to urge a ceasefire between Moamer Gaddafi's troops and rebels seeking to topple the strongman, as an anti-regime revolt entered a fourth month. The head of Britain's armed forces, meanwhile, said NATO should widen its bombing campaign to ensure Gaddafi doesn't manage to cling to power, while Pope Benedict XVI called for negotiations to end the violence. Khatib was received by Foreign Minister Abdelati Laabidi, who according to state news agency JANA told him of "serious violations" by NATO, which has been in charge of enforcing a UN-mandated no-fly zone over Libya since March 31. Laabidi "informed the UN secretary general's envoy of the extent of abuse and serious violations committed by NATO against the Libyan people in bombing civilian targets and inhabited areas in different Libyan cities," JANA said. The foreign minister also condemned the killing of civilians and the "assassination attempt" against Gaddafi, whose Bab al-Aziziya compound - where he resides - has been targeted by several NATO strikes in recent weeks. Soon after Khatib arrived, two loud explosions were heard in Tajura, an outlying suburb of the Libyan capital, a witness said. JANA reported that NATO air raids had on Sunday also targeted "military and civilian" sites in the city of Zuara, 120 kilometres (75 miles) west of Tripoli. UN chief Ban Ki-moon said earlier in the week that Khatib would hold talks in Tripoli with Prime Minister Baghdadi Mahmudi. Ban said he had urged Mahmudi on Tuesday to halt attacks on civilians immediately and called for "immediate verifiable ceasefire negotiations towards the peaceful resolution of the conflict and unimpeded access to humanitarian workers." General David Richards, Britain's chief of the defence staff, meanwhile told Britain's Sunday Telegraph that more military action was needed against the Libyan strongman. "The vice is closing on Gaddafi, but we need to increase the pressure further through more intense military action," he said. The general said he wanted NATO member states to support the targeting of Gaddafi's regime, not just targets which pose an immediate threat to civilians, such as tanks and artillery. "The military campaign to date has been a significant success for NATO and our Arab allies. But we need to do more. If we do not up the ante now there is a risk that the conflict could result in Gaddafi clinging to power," Richards said. "At present, NATO is not attacking infrastructure targets in Libya. But if we want to increase the pressure on Gaddafi's regime then we need to give serious consideration to increasing the range of targets we can hit." Protests against Gaddafi's 41-year autocratic rule began on February 15 and quickly escalated into a popular uprising, inspired by revolts in Tunisia and Egypt that toppled their respective hardline rulers. Gaddafi ordered his forces to crush the uprising, prompting an armed rebellion which has claimed thousands of lives while seeing much of eastern Libya fall into the hands of insurgents who have vowed to march on Tripoli and topple Gaddafi. On March 19, French, US and British forces, under a UN mandate to protect civilians, launched air strikes on Gaddafi's forces in a campaign that was taken over by NATO on March 31. The ICC chief prosecutor said on Sunday he was 'almost ready' for a Libyan rights abuse trial, as he prepared to apply for arrest warrants. Luis Moreno-Ocampo is expected to ask International Criminal Court (ICC) judges in The Hague to issue three arrest warrants on Monday, when the names of the accused could be revealed. Diplomats have said Gaddafi would likely head the list. "We are almost ready for trial," Moreno-Ocampo said in a statement. "The Office collected good and solid evidence to identify (those) who bear the greatest responsibility," he said. On the battlefield, rebels made new progress in their advance from the western port city of Misrata, which they freed in fierce fighting earlier in the week from a two-month siege by Gaddafi's forces. An AFP correspondent said they had moved 20 kilometres (12 miles) in the east to reach the gates of Tavarga and in the west they reached the gates of the city of Zlitan - their next main military target on the road to Tripoli. In the rebels' eastern bastion of Benghazi, Jalal al-Gallal, a spokesman for their National Transitional Council, touted the achievements of the past three months. "These three months have been very long," Gallal told AFP. "But we managed to secure the eastern areas, free Misrata and the mountainous regions in the west." He added: "Kahdafi's isolation is irreversible. And most importantly, we achieved freedom, freedom of speech, freedom of movement. Gaddafi's biggest mistake was failing to understand how important these were for us." But he also acknowledged that people in the east were losing patience that Gaddafi was still in power and that the military campaign against him had hit a stalemate. "It is true, people are impatient. And euphoria could drop a little bit," Gallal said. "After being optimistic, we have to start to be pragmatic. It is true, there could be some discontent."